Songs that are just mean, kind of hard to explain clearly, but you'll get the idea from the songs I list. Obviously this is opinion, but I'm sure we can agree on a few. Also, make sure it's GOOD rap, none of this half-pop bullshiit.
Pac and DMX are the two rappers that have multiple songs I think of right off the bat so I'll name a few...
2Pac - Hail Mary
2Pac - Ambitionz az a Ridah
DMX - Ruff Ryders Anthem (you could list half of this album honestly)
DMX - Bring Your Whole Crew
Plenty more coming... just though of this thread so I gotta do some thinkin...